The present disclosure relates to a storage element having a plurality of magnetic layers and performing recording using spin torque magnetization reversal and to a storage device using the storage element.
Concomitant with significant developments of various information apparatuses including mobile terminals, large capacity servers, and the like, elements, such as memories and logics, forming those apparatuses are also requested to improve performance, such as increase in integration degree, increase in operation speed, and reduction in power consumption. In particular, advancement in non-volatile semiconductor memories has been remarkable, and flash memories each functioning as a large capacity file memory have been increasingly in demand so as to replace hard disk drives.
In addition, in consideration of expansion into code storages and working memories, development of ferroelectric random access memories (FeRAMs), magnetic random access memories (MRAMs), phase-change random access memories (PCRAMs), and the like has been pursued in order to replace NOR flash memories, DRAMs, and the like, which are now commonly used. Some of those memories mentioned above have been already put into practical use.
In particular, since data is stored using the magnetization direction of a magnetic material, the MRAM is capable of performing high-speed and almost-infinite (1015 times or more) rewriting operations and has already been used in the fields of industrial automation, airplane, and the like. Because of its high-speed operation and high reliability, the MRAM is expected to be expanded into the code storage and the working memory in the future; however, in practice, there are problems to be overcome, such as reduction in power consumption and increase in capacity. These mentioned above are intrinsic problems resulting from the recording principle of the MRAM, that is, resulting from the method in which magnetization reversal is performed by a current magnetic field generated from a wire.
As one method to solve these problems, a recording method using no current magnetic field, that is, a magnetization reversal method, has been studied. In particular, researches on spin torque magnetization reversal have been actively performed (for example, see Japanese Unexamined Patent Application Publication Nos. 2003-17782 and 2008-227388, U.S. Pat. No. 6,256,223, Phys. Rev. B, 54, 9353 (1996), and J. Magn. Mat., 159, L1 (1996)).
A storage element of the spin torque magnetization reversal is frequently formed using a magnetic tunnel junction (MTJ) as in the case of the MRAM.
This structure uses a phenomenon in which spin-polarized electrons passing through a magnetic layer pinned in a certain direction impart torque (also called spin transfer torque in some cases) to another free magnetic layer (the direction of which is not pinned) when entering this free magnetic layer, and the magnetization of the free magnetic layer is reversed by passing a current equivalent to or more than a certain threefold value. Rewriting of 0/1 is performed by changing the polarity of the current.
The absolute value of the current for this reversal is 1 mA or less in an element having a scale of approximately 0.1 μm. In addition, scaling can be performed because this current value decreases in proportion to the element volume. Furthermore, since a word line for generating a current magnetic field for recording, which is necessary for the MRAM, is not necessary in this case, the cell structure can be advantageously simplified.
Hereinafter, the MRAM using the spin torque magnetization reversal will be referred to as the “spin torque-magnetic random access memory (ST-MRAM)”. The spin torque magnetization reversal may also be referred to as the spin injection magnetic reversal in some cases.